Objectives: Chronic physical inactivity contributes to the deaths of nearly 1 in 10 Americans. In seniors, the single most common life-threatening disease is congestive heart failure and for these patients, abnormalities of diastolic function play a critical role in the pathophysiology of their disease. The sponsor's research has demonstrated that healthy but sedentary aging leads to atrophy and stiffening of the heart with reduced myocardial and chamber compliance. In contrast, highly competitive senior runners had cardiac compliance that was indistinguishable from healthy young individuals suggesting that lifelong exercise training prevented this stiffening. However, prolonged and intense exercise training (4-6 hrs/wk for 1 yr) failed to restore cardiac compliance in healthy seniors despite other health benefits.